Traditional voice telephony products are typically band-limited to 4 kHz bandwidth using an 8 kHz sampling rate. These products, sometimes labeled as “narrowband”, include the telephone, data modems, and fax machines. Newer products aiming to achieve higher voice quality have doubled the sampling rate to 16 kHz to encompass a larger 8 kHz bandwidth, which is also known as “wideband” capable. The software implications of using a higher sampling rate are significant. Increasing the sampling rate not only increases the processing cycles needed, but also increases the memory used to store the data. In addition, software for systems supporting wider bandwidths and higher sampling rates must not preclude support for legacy band-limited functionality.
Increasing memory and processor cycles requirements is expensive because the memory and processing power footprints of digital signal processors (DSPs) are generally small. Implementing support for wider bandwidths thus requires creativeness to optimize memory and processor cycles, and in the means to support a variety of sampling rates.
In an environment with both narrowband and wideband devices, a voice call between a narrowband terminal and a wideband terminal cannot be accomplished by simply exchanging voice data streams. Voice telephony services such as conferencing require that the voice data streams from devices using different sampling rates be combined, so that each participant may hear the voices of all other participants. Combining the digital audio streams from a narrowband terminal with a lower sampling rate and a wideband terminal with a higher sampling rate requires that adjustments be made to the voice data streams to allow them to be combined. It is also necessary that the resulting combined voice data stream be made available in a form acceptable to each participant's terminal, whether it uses a lower or higher sampling rate.
Accordingly, there is a need for switchboard functionality that can support the interconnection of both narrowband devices and wideband devices.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.